UK Multi-Inverter Commercial Solar Export Control Setup Guide

Key Takeaways

• Commercial solar installations in Great Britain must comply with specific grid codes like G99 and G100 for connection and export control.
• The Distribution Network Operator (DNO) has a duty to connect, but this is subject to terms and compliance with safety regulations.
• Loss of Mains (LoM) protection, including Rate of Change of Frequency (RoCoF) settings, is a legal requirement for generators.
• Non-compliance with grid codes can lead to de-energisation of generation assets; engaging an accredited installer is crucial.

Understanding Commercial Solar Export Control in Great Britain

Connecting a multi-inverter commercial solar system to the grid in Great Britain requires adherence to specific technical and legal requirements, particularly concerning export control. These rules ensure grid stability and safety. The Distribution Network Operator (DNO) in your area manages these connections.

An electricity distributor is under a duty to make a connection between a distribution system of theirs and any premises, when required to do so by the owner or occupier of the premises or an authorised supplier acting with consent. This duty includes providing necessary electric lines or electrical plant. However, these duties are performed subject to agreed terms and can be subject to exceptions, such as circumstances not within the DNO's control or if it would involve breaching regulations.

Grid Connection Standards: G98, G99, and G100

Commercial solar installations in Great Britain must comply with Engineering Recommendations (EREC) issued by the Energy Networks Association (ENA). These standards dictate how generation equipment connects to the distribution network and how export is managed.

• G98 Micro-Generation and Storage Connections: This standard applies to connecting generation, including energy storage, at 16 amps or less per phase, for a single or multiple premises.
• G99: This is a legal requirement for certain generators connecting to the distribution networks on or after 27 April 2019. It covers the requirements for the connection of generation equipment, including commercial solar systems, to the grid.
• G100: This standard details the technical requirements for customers' export and import limitation schemes. It is applicable after 1 May 2023 and is critical for any commercial solar installation that needs to limit its export to the grid.

Manufacturers list devices compliant with these standards on the ENA Type Test Register. This register allows manufacturers to upload and maintain data and documentation for devices covered by G98, G99, and G100 standards.

Loss of Mains (LoM) Protection and RoCoF Settings

Loss of Mains (LoM) protection is a safety feature designed to check if a generator is still connected to the supply network. If the grid connection is lost, LoM protection disconnects the site to prevent unsafe operation (islanding).

The Rate of Change of Frequency (RoCoF) is a key component of LoM protection. RoCoF detects the absence of the connection to the system and disconnects the site if that RoCoF exceeds a specific value. For updated EREC G59 requirements, the RoCoF setting has been changed to 1Hz/s with a definite time delay of 500 milliseconds.

Non-compliance with updated EREC G59 requirements breaches the terms of the connection agreement and is a legal requirement. All generators connected to distribution networks in Great Britain have Loss of Mains protection. Where LoM is provided by vector shift, it must be removed and/or replaced with RoCoF.

Compliance Status and Potential Faults

The ENA Type Test Register provides status updates for devices, indicating their compliance with current standards. Understanding these statuses is important for ensuring your equipment is approved for connection.

Failure to maintain compliance can lead to serious consequences:

• Generator non-compliance with EREC G59: Failure to update LoM protection to meet updated G59 requirements (e.g., replacing vector shift with RoCoF at 1Hz/s with 500ms delay) can result in enforcement action.
• De-energisation of generation assets: If no evidence of compliance is provided or is insufficient, the DNO will make arrangements to de-energise the generation site's Connection Point in accordance with Distribution Code DGC12. Any generators who are not compliant and therefore require updates to their protection will be subject to an enforcement programme which could ultimately result in the de-energisation of generation assets.
• Connection offer invalidation: Failure to pay connection offer expenses within 30 days of invoice can invalidate the connection offer.

What you can check yourself, and what you cannot

As a system owner, you can ensure that your chosen inverters and other generation equipment are listed as compliant on the ENA Type Test Register. You can also ensure that your accredited installer has submitted all necessary documentation to your DNO.

You cannot, however, change inverter settings related to grid protection yourself. Grid-protection settings, such as RoCoF, are set by an accredited installer during commissioning to comply with DNO requirements. Changing these settings without proper authorisation can breach your connection agreement and compromise grid safety. If you believe there is an issue with your system's grid protection settings, contact your accredited installer or DNO.

What the published sources do not tell you

While the ENA and DNOs provide extensive guidance, specific details on application forms for G98 and G99 are often mentioned without direct links to the forms themselves in publicly available material. The full "Connections Charging Statement" for DNOs, which details the balance payable on acceptance of quotes, is also typically a separate document.

Furthermore, specific technical details for implementing multi-inverter export control via a centralized plant controller (Modbus TCP) or grid meter synchronization for zero-export failover are not universally published by DNOs. These implementation details are typically handled by the inverter manufacturers and system integrators, often requiring proprietary software or specific hardware configurations that are beyond the scope of general DNO connection guidelines. DNOs specify the requirements (e.g., G100 for export limitation) but not the method of achieving them.